1. Field of the Invention
The present invention relates to metallic soap fine particles. More particularly, it pertains to metallic soap fine particles that are extremely fine and have a narrow particle size distribution, to a process for producing the aforesaid metallic soap fine particles in a simple, easy and efficient manner and to the utilization of the aforesaid metallic soap fine particles as a toner additive and a cleaning aid for use in an image recording apparatus.
2. Description of the Related Arts
Metallic soap has heretofore been widely utilized in a large variety of fields including electronic printing, powder metallurgy, cosmetics, coating materials and resin processing. With the recent progress in a great deal of advanced functionalization in these fields, further fineness or hyperfineness has come to be required of the metallic soap so as to meet the above-mentioned requirement of advanced functionalization.
Typical examples of processes for producing metallic soap that are carried out at the present time, include a process in which a solution of an inorganic metal compound is added dropwise to a solution containing an alkali metal salt of a fatty acid to cause a reaction (double decomposition process) and a process in which a fatty acid is reacted with an inorganic metal compound under kneading at an elevated temperature (fusion process). However, the metallic soap obtained by any of these processes has an average particle size larger than 7 .mu.m and further has a ratio by weight of particles having a particle size of 10 .mu.m or larger to the whole particles of the metallic soap being more than 20% . Consequently, when any of these processes is employed, it is impossible to efficiently produce matallic soap having an average particle size of 4 .mu.m or smaller. There is disclosed a continuous process capable of producing metallic soap fine particles having an average particle size in the range of 5 to 10 .mu.m (Japanese Patent Application Laid-Open No. 299247/1989(Hei-1). Nevertheless, the abovementioned process is not necessarily satisfactory in order to efficiently produce metallic soap fine particles having an average particle size in the range of 4 .mu.m or smaller. Under such circumstances, an attempt is made to develop a process capable of producing further fine metallic soap by pulverizing and classifying the aforesaid metallic soap. However, with the present state of the art it is quite difficult to obtain matallic soap having an average particle size of 4 .mu.m or smaller by means of classification. In addition, when the aforesaid classification method is used, the product yield is reduced as low as 10% or less and besides, it is made difficult to selectively produce the particles having a size of 10 .mu.m or smaller. Moreover, the repeated pulverization and classification cause destruction of the surface of the metallic soap fine particles. Consequently, such destruction deteriorates the surface smoothness of the metallic soap fine particles and increases the friction coefficient among said particles, thereby lowering the powder fluidity of the metallic soap.
On the other hand, the application fields utilizing such metallic soap fine particles are exemplified by toner particles and a cleaning aid in an electrophotographic copying machine.
A variety of methods for use in electrophotographic copying machines are known as described in U.S. Pat. No. 2,297,691 and Japanese Patent Publication Nos. 23910/1967 (Sho-42) and 24748/1968 (Sho-43). In general, the foregoing methods comprise the steps of forming an electric latent image on a picture image support by any of various methods through the utilization of a photoconductive material; developing said electric latent image by the use of a toner; and at need transferring and fixing said image on a recording medium such as a sheet of paper or a polymer to obtain a sensible picture image. The picture image support after the transfer is used repeatedly, after the toner remaining on the surface thereof has been removed. A variety of methods have heretofore been proposed as a development method by using a toner, such as a method for fixing a toner image and a method for cleaning the toner remaining on a picture image support. The method suited to the respective image forming process is adopted from the variety of methods.
There have heretofore been proposed, as a process for producing a toner to be used for these purposes, a process for producing toner fine particles in which a colorant such as a dyestuff or pigment is melt mixed with a thermoplastic resin in general and is uniformly dispersed therein, and the resultant uniform mixture is turned into toner fine particles having a desired particle size by the use of a pulverizing apparatus and a classifying machine as disclosed in Japanese Patent Application Laid-Open No. 276764/1992 (Hei -4) and a process for producing toner fine particles by uniformly dissolving or dispersing a polymerizable monomer, a colorant and a polymerization initiator, and as necessary, a crosslinking agent and/or a charge contolling agent, and thereafer turning the resultant monomer composition into toner fine particles by means of suspension polymerization method as described in Japanese Patent Publication Nos. 10231/1961 (Sho-36) 10799/1968 (Sho-43) and 14895/1976 (Sho-51).
The toner produced by any of these procsses is usually used in an electronic copying apparatus, an electrostatic printer and the like. Moreover, the high densification and colorfulness of printing in recent years have come to call for improvement in preservation stability of toner particles; for enhancement in the speed and precision of visible image formation of a toner for a picture image support; for enhancement in the speed and precision of transfer of an visible image from a picture image support to a recording medium; for enhancement in the speed and precision of fixing the visible image; and also for enhancement in the speed and precision of cleaning for the toner remaining on the picture image support. Accordingly, advanced characteristics higher than anything before have required of a toner for use in an electronic copying apparatus and of an additive for use in a cleaning aid.
It has hitherto been known that improvements can be made in blocking resistance of a toner, in fluidity thereof, in eliminability from an toner image support or in cleaning properties by adding metallic soap such as zinc stearate or calcium stearate to a toner or a cleaning aid. For example, the cleaning performance for a picture image support is improved by adding metallic soap as a cleaning aid to a toner as disclosed in Japanese Patent Application Laid-Open Nos. 111576/1982 (Sho-57), 225870/1985 (Sho-60), 106780/1990 (Hei-2) and 269478/1991 (Hei-3). Further there is known a cleaning method for a picture image support using a cleaning brush or a blade which has previously been used, in which method the surface of the picture image support is coated with metallic soap of a saturated fatty acid or metallic soap of an unsaturated fatty acid as a cleaning aid, as disclosed in Japanese Patent Application Laid-Open No. 73774/1982 (Sho-57). The above-mentioned cleaning method makes it possible to alleviate the friction on the picture image support due to a cleaning brush or a blade by said coating and at the same time, makes it possible to facilitate the eliminability of foreign matters stuck to the picture image support.
However, metallic soap containing large-size particles, when added to said toner fine particles internally or b externally, fails to sufficiently be dispersed in said toner fine particles. In addition, the metallic soap containing large-size particles exerts such evil influences on the toner and image support, etc. as described in the following: The reproducibility of the toner fluidity is lowered, and the accuracy or precision of the visible image formation is made insufficient; the service life of the image support is shortened by the abrasion or frictional damage due to the large-size particles contained in the metallic soap at the time of forming visible image of the toner on the the image support; the service life of the image support is shortened by the abrasion or frictional damage due to the large-size particles contained in the metallic soap at the time when the image support is coated with metallic soap as a cleaning aid which has conventionally been used; and accordingly, sufficient image density is made impossible to obtain during a long-term running and besides, a vivid image is made difficult to obtain over a long period of time.
On the other hand, the fields utilizing such metallic soap fine particles are exemplified by the fields of powder metallurgy, cosmetics, coating materials and resin processing, respectively in addition to the above-mentioned field of an electronic printing.
The metallic soap is generally used as a fluidity improver for metallic powders in the field of powder metallurgy. In recent years, further particle size reduction for metallic powders and fineness of a firing mold have been progressing in the field of powder metallurgy. However, the conventional metallic soap, when used for said purpose of use, fails to be sufficiently uniformly dispersed in metallic powders, since said metallic soap powders have large particle sizes as compared with those of the metallic powders, and also have a high content of particles larger than 10 .mu.m. As a result, unfavorable problems take place in that the fluidity of metallic powders in a mold becomes insufficient and in particular, the strength of filaments as well as production efficiency are lowered in the case where fine metal processing such as filament processing is required.
Moreover, metallic soap is generally used as a pigment dispersant in the field of coating materials. Accompanying further film-thinning in recent years, it is desired in this field that improvements be made in the smoothness of coating surfaces, in sliding property of coating surfaces and in water repellency of film and coating. However, conventional metallic soap, when added to a coating material, brings about such hindrances and troubles as described hereunder: it is made difficult thereby to obtain a coating in which the metallic soap is uniformly dispersed by reason of insufficient dispersibility of the metallic soap in the coating material; sliding property and water repellency to be imparted to the coating by the metallic soap are made insufficient thereby; and besides the surface smoothness of the coating is impaired by the adverse influence of the large-size particles of the metallic soap in the case of forming a coating having a thickness of 10 g m or smaller.
Moreover, metallic soap is generally used as a stabilizing agent and processing aid in the field of resin processing. However, conventional metallic soap, when added to a resin at the time of its processing, gives rise to the following hindrances and troubles as pointed out in said field: The resin processing takes an unreasonably long hours by reason of insufficient dispersibility thereof in resin powders and the like; and the processed resin suffers from white turbidity and decreases in strength and product yield because of insufficient dispersibility of the metallic soap in the processed resin product.
It is forced to say by the troubles and disadvantages as described hereinbefore that the application of the conventionally used metallic soap to the foregoing fields causes extreme difficulty. Such being the case, it has eagerly been desired in the foregoing fields to develop novel metallic soap which has an average particle size markedly smaller than that of the conventionally used metallic soap and which is minimized in the content of large-size particles, more specifically novel metallic soap hyperfine particles which has an average particle size of 4 .mu.m or smaller and which is minimized in the content of particles having sizes of 10 .mu.m or larger. It is extremely difficult, however, to efficiently produce metallic soap fine particles by the use of the conventional processes for producing, pulverizing and classifying the conventional metallic soap. Thus it has hitherto been desired to develop a practical production process for efficiently producing the metallic soap having hyperfine particles. In order to produce the same to be used for the foregoing purposes, it is ideal to develop a process capable of containing, as much as possible, metallic soap fine particles having particle sizes of 4 .mu.m or smaller upon the completion of the synthesis by dispensing to the utmost with a pulverizing step for the synthesized product.